Automotive fuel line tubing and hoses include both monolayer and multilayer materials. Traditionally, metals were used to form fuel lines, but automotive manufacturers have been replacing metals wherever possible to reduce weight and CO2 emissions. More recently, fuel line tubing and hoses have been formed of aliphatic polyamide (PA), high-heat rubber composites, and braided polytetrafluoroethylene (PTFE). Unfortunately, these materials have often provided less than ideal performance and/or required complex and costly formation techniques. For example, while braided PTFE and high heat rubber composites can be used in high heat environments, the constructions are often complex and costly. The use of aliphatic polyamide also has limitations. For instance, PA12 has limitations with regard to both permeation of fuel and long term heat aging at the higher temperatures present in newer vehicles. Thus, fuel lines formed of these materials often require a heat shield at added weight and cost. In addition, multi-layer constructions of these materials are often subject to delamination, especially where fluoropolymer layers are present, and generally require special chemical bonding between layers.
There are multiple different requirements for the lines in the fuel system, some of them varying depending upon the final application. For example, in the vapor line, a good barrier property must be provided to prevent vapors from escaping into the environment. In addition, there are thermal and mechanical requirements that should be maintained over a long lifetime. Included in the mechanical requirements are sufficient flexibility and impact strength for both fabrication and safety. In addition to the requirements for vapor lines, liquid lines also meet the requirement that essentially no materials used in forming the fuel line contaminate the fuel, which could lead to problems such as clogged fuel injectors. Thus, the lines must be chemically resistant to the liquids to be carried by the lines. Many polymers that have been examined for use in forming fuel lines to date have leached oligomers that can clog the fuel system and reduce engine performance.
Polyarylene sulfides are high-performance polymers that may withstand high thermal, chemical, and mechanical stresses and are beneficially utilized in a wide variety of applications. Polyarylene sulfides have often been blended with other polymers to improve characteristics of the product composition. For example, elastomeric impact modifiers have been found beneficial for improvement of the physical properties of thermoplastic compositions. Compositions including blends of polyarylene sulfides with impact modifying polymers have been considered for high performance, high temperature applications.
Unfortunately, elastomeric polymers generally considered useful for impact modification are not compatible with polyarylene sulfides and phase separation has been a problem in forming compositions of the two. Attempts have been made to improve the composition formation, for instance through the utilization of compatibilizers. However, even upon such modifications, compositions including polyarylene sulfides in combination with impact modifying polymers still fail to provide product performance as desired, particularly in applications that require both high heat resistance and high impact resistance.
What are needed in the art are thermoplastic compositions that can be used to form automotive fuel lines that exhibit excellent barrier properties as well as good mechanical characteristics, including both good impact resistance and good flexibility, so as to form fuel lines that can be quickly and easily installed and that can exhibit desirable characteristics over a long working life.